Scavenger for Primary Amines in the Presence of Secondary Amines

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Biotage® PS-Benzaldehyde resin is useful for removing nucleophiles from solution, including primary amines (selectively, even in the presence of secondary amines), hydrazines also carbon-based nucleophiles such as Meldrum’s acid and organometallics.

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English

PS-Benzaldehyde is the resin-bound equivalent of benzaldehyde. This resin is useful for scavenging various nucleophiles, including primary amines (selectively compared with secondary amines), hydrazines and also carbon-based nucleophiles such as Meldrum’s acid and organometallics.Tags: Product Notes

Background

PS-Benzaldehyde is the resin-bound equivalent of benzaldehyde and is useful for scavenging various nucleophiles, including primary amines (selectively compared with secondary amines), hydrazines, also carbon-based nucleophiles such as Meldrum’s acid and organometallics.

The capacity of PS-Benzaldehyde is 1.2 mmol/g, based on phenylhydrazine uptake. Scavenging reactions typically use 3 equivalents of resin per equivalent of substrate to be scavenged. Various solvents can be used, including DCE, DCM, and DMF with a temperature range from 20 to 50 ˚C. PS-Benzaldehyde is stable at room temperature with no loss of activity observed over an extended period.

Representative Procedure

Phenylhydrazine Scavenging

PS-Benzaldehyde resin (3 equivalents) in DCE was allowed to react with phenylhydrazine (1 equivalent) in the presence of a catalytic amount of glacial HOAc. The reaction was monitored by TLC and was complete after stirring for approximately 1 h at room temperature. The reaction may also be run without HOAc by heating for 1 h at 50˚C.

Scavenging Various Substrates

PS-Benzaldehyde (3 equivalents) was added to a solution of the substrate in DCE along with a catalyst if necessary. The mixture was stirred for the specified time and temperature, and the filtrate was analyzed by TLC for disappearance of the substrate by comparison with analytical standards.

Reductive Alkylation of Primary Amines

A THF solution (0.50 M) of N-(3-aminopropyl)morpholine (1.2 mL, 0.60 mmol) was added to a THF solution (0.50 M) of 1,4-cyclohexanedione mono-ethylene ketal (1.0 mL, 0.50 mmol). MP-Triacetoxyborohydride (2.0 mmol/g, 0.625 g, 1.25 mmol) was then added and the mixture was agitated for 16 h at room temperature. When the reaction was complete, PS-Benzaldehyde (0.42 g, 0.5 mmol) and THF (2 mL) were added and the mixture was further agitated for 6 h. The resin was filtered and washed with THF (2 x 4 mL). The combined solution was concentrated to afford the product secondary amine as the acetate salt in 77% yield and 100% purity. The secondary amine was characterized by gas chromatography and H NMR.

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